The present invention relates to a process for the production of an articulated monolithic composite panel and the obtained panel, which have mechanical characteristics suitable more particularly in the transmission of forces, particularly for application to the fan hatches of turbo reactors or landing gear doors.
Certain elements of an aircraft are subjected to particular mechanical stresses because they are movable and/or dismountable and are in contact with the outside, which requires high resistance to shocks.
Moreover, being mounted on aircraft, these elements must remain light and insensitive to the loss of technical or service fluids: water, oil, hydraulic fluid.
The panel constituting the element must resist fire and satisfy various standards which establish minimum resistance tests in case of deterioration or rupture of a part constituting said element.
The elements recited above such as hatches are at present made essentially by three processes:
composite sandwich structure,
metallic monolithic structure, and
composite or hybrid monolithic structure.
Throughout the description and the claims, there will be meant by xe2x80x9cmonolithicxe2x80x9d a sheet, leaf or plate, of a single ply or composed by several assembled plies secured directly to each other, without interposition of a core of cellular material as in a sandwich panel.
The composite sandwich structure is interesting from the point of view of the weight because it comprises an aerodynamic external skin of small thickness, and an internal similarly thin skin, between which is interposed a core of a porous material such as honeycomb, these three constituents being secured together.
It will be noted that the skins are thin because the sandwich structure permits easily achieving the desired general mechanical resistances. This is also a drawback because the skins are intrinsically fragile and have low resistance to impact, particularly the external skin. Moreover, there must be added protections against fire and lightning to meet the technical and regulatory requirements.
As to the sandwich structure itself, it will be noted that in case of loss, the core of porous material or of foam soaks up fluids and can give rise to certain accumulation which it is sought precisely to avoid.
These sandwich structures are also relatively difficult to repair because the weight of a repair plate of polymeric or metallic material with riveting is delicate, which is not satisfactory in the case of aircraft, for users and for maintenance services.
The metallic monolithic structure has inherent defects as to material, particularly an unfavorable mass balance. Moreover, it is necessary to rivet the reinforcing frames directly on the metallic plates and risk of corrosion remains.
Moreover, when there are movable elements such as hatches or flaps, it is often difficult to position the frame used whilst ensuring good alignment of the metal hinges. Generally, the frames are fishtailed on the hinges to transmit the various forces to which the movable member is subjected.
The composite or hybrid monolithic structure comprises a single skin reinforced by a frame with composite or metallic stiffeners connected to said skin by rivets or cement.
In this case, it is difficult to position the hinges unless the skin is of a thickness greater than that which is necessary, to permit the absorption of sharp forces.
This is prejudicial to the weight and to the cost.
Another problem arises when it is necessary to provide emplacements to position the access ports, inspection doors or ventilating grilles or other members in these movable elements which are made of composite material.
It will be understood that the positioning of the access door, the inspection port and/or grille is determined by the position of the member to be inspected.
However, the positions of the hinges also require precise positioning, determined by the manufacturer, which leads to particular problems when the frame provided for absorbing forces from the hinges coincides with an access port, an inspection door or a ventilating grille. The invention provides a solution to this problem.
Thus, the present invention has for its object a process for the production of a monolithic composite panel provided to be articulated on a support, particularly a panel articulated by means of hinges for providing a fan hatch of a turbo reactor or a landing gear door in an aircraft, said panel comprising openings for emplacement of service elements such as access doors, ports and/or ventilating grilles, characterized in that it consists in providing a network of beams, as a function of said openings, avoiding the emplacements of the surface elements, shaped and positioned for taking up and transmitting forces particularly between the articulation means and the panel. Such means are more particularly axial and circumferential beams.
Certain axial beams can be curvilinear and/or of variable cross-section along their longitudinal axis.
The process comprises more particularly the following steps:
draping over a mold of the shape of a panel to be obtained, of at least one ply of composite material to form a plate of a shape complementary to that of the mold,
emplacing on one of the surfaces of the panel, according to the predetermined network, cores of a cellular or foam material, avoiding the reserved openings,
draping on these cores at least one ply of a composite material covering partially the plate to form resistant beams, and
baking to polymerize, in one or two steps.
It is possible to add a ply of material which is highly conductive, between the mold and the first ply.
The invention also has for its object the articulated monolithic composite panel obtained by the practice of the process as well as the hatch particularly for equipping an aircraft such as a fan hatch of a turbo reactor or such as a landing gear door made from this panel by practice of the process.
There is known from U.S. Pat. No. 4,471,609 a hatch of composite material of the xe2x80x9ccore cowlxe2x80x9d type, which is to say for protecting the core of a motor, which is different from a xe2x80x9cfan cowlxe2x80x9d which is a hatch for protecting the fans. The technical requirements involved are different as a function of the location. In this U.S. patent, the hatch is used to limit the bending deformation of the motor of the portion located in the very hot region, whilst absorbing large forces. The hatch described in this patent has no door or access port because the equipment to which access must be had is located outside these very hot regions.